Beltré was signed out of the Dominican Republic by the Los Angeles Dodgers in 1994 by Ralph Avila, the grandfather of Detroit Tigers all-star Catcher Alex Avila . Beltré attended Liceo Maximo Gomez High School. In 1994, while working out at Campo Las Palmas, a Los Angeles Dodgers facility, he was spotted by scouts Ralph Avila and Pablo Peguero. Though only 15 and weighing just 130 pounds, he had a quick swing and live throwing arm. On the insistence of Avila and Peguero, the Dodgers signed Beltré in July. He received a $23,000 bonus. When it was revealed that Beltré had signed his initial contract at the age of 15, commissioner Bud Selig suspended the Dodgers' scouting operations in the Dominican Republic for a year, because signing a player at that age was prevented under MLB rules.[2]

After being called up to the majors from the then Dodgers Double-A affiliate San Antonio Missions, Beltré made his major league debut on June 24, 1998, starting at third base in the first game of an interleague series against the Anaheim Angels. At the time, he was the youngest player in the National League.[3] During his first at-bat, Beltré smashed a two-out RBIdouble off Angels starterChuck Finley into left field to score Paul Konerko from second base to tie the game. He would hit his first home run six days later against Texas Rangers starter Rick Helling. At the end of the 1998 season, Beltré would finish with 13 errors at third base while batting .215 with seven home runs.

Beltré hit .265 while hitting 18 homers a year (on average). From 1999 through 2003, Beltré also started 710 games at third base (out of 810 games played) averaging a .948 fielding percentage.

Beltré was signed by the Seattle Mariners as a free agent before the 2005 season to a five-year, $64 million deal.[5] Regressing to his pre-2004 form, he batted just .255 with 19 home runs and 87 RBIs. Manager Mike Hargrove did not give up hope on Beltré, saying, "I think it's a season that, personally, he's disappointed in. I think it was a year that he will improve on the longer he's here and the longer he's in the American League."

Beltré fielding

After batting .167 through April 10, Ted Miller of the Seattle Post-Intelligencer wrote that Beltré may become one of the Mariners' greatest busts.[6] By June 5, 2006, Beltré's batting average was slowly improving, from .109 on April 16 to .236 at that time. After hitting his first home run in April, and his second later that month, Beltré's hitting began to improve.

Though it was not a great season for Beltré, it was statistically his best as a Mariner. He hit .276, had 26 home runs, and had 99 RBIs. He also had a career high 41 doubles. He also was honored with a Fielding Bible Award for being the top MLB defensive third baseman during the year.[8]

The 2007 season was not one of Beltré's better defensive years statistically.[9] In 2007, he tied with Brandon Inge for the AL lead in errors by a third baseman, with 18, but Beltré ranked second in the league in assists, total chances, and range factor. He also had the lowest fielding percentage of all third basemen in the league, .958.[9][10] Beltré was awarded the Gold Glove award

On January 7, 2010, Beltré signed a one-year, $9 million deal with the Boston Red Sox, which had a $5 million player option for 2011 with a $1 million buyout.[20]

Beltré led the Red Sox in batting average (.321) in 2010 and tied David Ortiz for the team lead in RBIs (102). He finished the year with 189 hits in 589 at-bats. He had 28 home runs and 84 runs scored. Beltré led the Majors in doubles, with 49 (also a career high). He also finished fourth in the AL in batting average, and was fifth in the AL in total bases (326) and slugging percentage (.553). He also had two stolen bases on the year, and finished ninth in the MVP voting.[21] On defense, he tied for the AL lead in errors by a third baseman, with 19.[22]

On January 5, 2011, Beltré signed a five-year (2011–15), $80 million contract with a vesting option for $16 million for the 2016 season with the Texas Rangers. He was on the 2011 American League All-Star team.[3] On July 22, Beltré strained his hamstring and was also placed on the DL. On September 4, Beltré hit a line single to right against the Boston Red Sox for his 2,000th career hit. On September 11, Beltré hit two home runs, including the 300th of his career, against the Oakland Athletics.

In 2011, Beltré batted .296 with 32 home runs (5th in the AL).[3] He was third in the American League in slugging percentage (.561), sixth in RBIs (105), and ninth in OPS (.892).[3] Through 2011, he led all active third basemen in career putouts (1,660) and errors (235).[3] He won his third Fielding Bible Award for his outstanding defense.[23]

Beltré once again proved to be one of the best third basemen in the league, being voted to the 2012 Major League Baseball All-Star Game on July 1, 2012 as a starter along with teammates Josh Hamilton and Mike Napoli. This was his third all-star game and third in a row dating back to 2010 with the Boston Red Sox. As of August 28, his numbers compiled are: .315 avg., 25 HR, 81 RBIs, and an .881 OPS.[29]

On August 22, 2012, in a game against the Baltimore Orioles, Beltré hit three home runs in his first three at-bats, including two in the same inning. He joined Pablo Sandoval, Albert Pujols, George Brett, Reggie Jackson and Babe Ruth as the only players to have a three-homer game in the regular season and the postseason.[30] On August 24, he hit for the cycle for the second time in his career. Both of his cycles came at Rangers Ballpark (his first was as a member of the Mariners), the only time in MLB history that this has happened.[31] He joined Joe DiMaggio as the only two players in big league history to have a three-homer game and a cycle in the same week. For his efforts, Beltré was named the AL Player of the Week for the week of August 20–26. During the seven games he hit .433 (13-for-30) with three doubles, one triple, five home runs, nine RBIs and seven runs scored. He had the highest slugging percentage (1.100) for the week in the majors, the most total bases (33), was tied for first in hits and home runs, and tied for second in RBIs.[32] For the season, he won his second straight Fielding Bible Award and fourth overall.[33]

On July 8, 2013, Beltré was named the American League Player of the Week for July 1–7. Beltré batted .478 (11-for-23) with 4 homers, 2 doubles and 5 RBI in 6 games last week. He led the American League in home runs, slugging (1.087), OPS (1.607), total bases (25), and extra-base hits (6) while producing the fourth highest batting average. Beltré hit safely in all six games with two or more hits four times. He had the 24th multi-homer game of his career with a pair of long balls on July 4, 2013 against Seattle.[35]

On August 5, 2013 Beltré was named the American League Player of the Month for July 2013, his third such honor with the Rangers. Beltre batted .369 with four doubles, nine homers, 19 RBIs and 13 runs scored over 26 games. He tied Alfonso Soriano for the Major League lead in homers and tied with Torii Hunter for the MLB lead in total bases (69). Beltre also finished among the AL leaders in slugging percentage (second, .670), hits (tied for second, 38), extra-base hits (tied for fourth, 13), RBIs (tied for fifth) and batting average (sixth). Just for good measure, Beltré capped off his award-winning month in style, blasting a walk-off homer to lead the Rangers past the Angels on July 31. Beltré has received AL Player of the Month honors four times, most recently with the Rangers in September 2012. He is one of seven players to win the monthly award multiple times with Texas, joining Josh Hamilton (four), Rafael Palmeiro, Alex Rodriguez (three each), Ivan Rodriguez, Juan Gonzalez and Ruben Sierra (two apiece).[36]